Keyboard pedals--the two cent version

Adding pedals to your keyboard depends on the kind of keyboard you are
using. Most (probably 99% or more) keyboards today are the membrane
style, which consists of two mylar sheets with silver-ink lines
printed on them, and a spacer with holes between the sheets. [Older
"quality" keyboards, like those on the original IBMs and Apples had a
switch-per-key...they feel soooo nice but they are expensive. Kinesis Professional QD keyboards, for
example, still use a switch-per-key design and cost around $300.]

Anyways, these mylar sheets in a membrane keyboard bond to a
circuit board with a microcontroller that is the brains of the
keyboard. The silver inked wires on the mylar sheets are equivalent to
an x-y matrix (it doesn't look like it from the sheets, but one sheet
has the "X" wires and the other has the "Y" wires). The
microcontroller detects if a key is pressed when an X wire is mashed
onto a Y wire by a finger depressing the flexible plastic membrane
through a thin spacer.

If you want to add a pedal that acts like a particular key, all you
need to do is trace the silver ink wires for the X,Y pair that defines
the key back to the corresponding pin on the main circuit board. You
can make this job easier by using a marker and drawing out the path on
the back side of the mylar sheet (doing it on the printed side
may render your keyboard non-functional). Then, solder a pair of wires
to the connections on the main circuit board that connect the pedal in
parallel with the keyboard switch. The pedal should, of course, be a
normally open switch of some kind. Music stores sell all kinds of good
footpedals for musical keyboards. They usually terminate at quarter
inch jacks, so you can just drill a hole in your keyboard and mount a
quarter inch jack on the side of your keyboard and run the wires to
the main circuit board internally--it'll look like it was always meant
to be there. It will also be robust and easy to take apart when you
want to move the keyboard.

Don't try soldering to the mylar sheets themselves, they will melt.
Solder to the main circuit board instead! Also, don't get your finger
oils on the silver ink, as the ink will corrode with time. It's a
subtle thing, so you don't have to do this work with gloves and
tweezers, but at the same time eating pizza and smearing grease
all over the traces is No Good (TM).

Finally, don't lose any screws to the metal sheets that are used to
press the membranes together (most keyboards I've taken part use some
sort of backing mechanism consisting of a metal sheet with a bazillion
screws in them). The quality of the keyboard and ease of activating a
key depends on the backing being solidly in there so the membranes
deform in the right way. Also, be careful when flipping the half of
your keyboard with the keycaps...some designs have the keycaps loose
and you'll end up scattering keycaps everywhere!

Good luck -- bunnie (c) 2/18/2002

As usual, I am not
responsible for any damages incurred to your keyboard if you try this
and it doesn't work...caveat hacker!